Things Vanitas is vulnerable to: Sleep, Gravity. Things that are like Gravity; an Aero spell to the face when you're not expecting it and a long drop. He ends up hitting the courtyard tiles on his back with a winded 'oof'.

He lies there for a bit seeing stars but gets up pretty quickly when he does move, and Void Gear happily vanishes from the now be-holed wall to Vanitas's pissed off hand. The space kind of stymies the idea of getting it out so he can think, so he presses down on it and simmers up at Ventus.

"If I wanted to kill you you're be dead, idiot!" He yells back up. No. No he wouldn't be, Vanitas. "Oh sorry, am I interrupting something?" What is so important you can't have a nice uncivil conversation. Honestly he's had some inoculation from meeting canon Ventus, but this Ventus is weirder again. His Ventus is never busy, because he just kind of sits in his room all the time. "I don't care about Xehanort!"
Vanitas both does, and doesn't want to fight him. He will never admit it, but he holds fear towards the man; being turned into a popsicle will do that. If the others were with him... his fingers twitch towards his pocket but don't go in.